a vast war within radical Islamist forces

The movement is led now by an elusive figure named Abu Bakr al-Baghdadi. Reflecting its expanding turf, A.Q.I. changed its name to the Islamic State in Iraq and al-Sham. Zawahiri urged ISIS to stay out of Syria, leaving it to the designated Al Qaeda affiliate, Jabhat al-Nusra. Characteristically, ISIS engaged in shocking brutality, even against rival Islamist groups. In 2013, it took over the provincial capital of Raqqah, in northern Syria, on the banks of the Euphrates—the first real victory in the rebellion—and once again drew many foreign jihadists to its cause. Zawahiri couldn’t tolerate the insubordination of Baghdadi’s troops, and in February of this year Zawahiri booted ISIS out of the Al Qaeda consortium. By that time, ISIS had returned to Iraq and taken over Fallujah, the first major city in the country to fall under its rule.

According to one estimate, in the Long War Journal, ISIS now controls a third of Iraq. The strike has been so sudden and surprising that other forces haven’t yet responded, but they will. And then the long-sought goal of Zarqawi and his progeny—a vast war inside Islam—will become a reality.